Process for treating ores containing arsenic.



UNITED sTATEs PATENT oEEIoE.

THOMAS BURNS MCGHIE, OF LONDON, ENGLAND, ASSIGNOR OF ONE-HALF TO THOMASBARTON, OF LONDON, ENGLAND.

Specification of Letters Patent.

Patented April 21, 1908.

Application filed September 9, 1907; Serial No. 392,049.

To all whom it may concern:

Be it known that I, THOMAS. BURNS Mo- GHIE, metallurgist, a subject ofthe King of Great Britain, residing at 9 Gracechurch street, in the cityand county of London, England, have invented a new and useful Processfor Treating Ores Containing Arsenic, of which the following is aspecification.

The present invention relates to improve ments 1n the treatment ofarsenical minerals and the partly smelted substances known as speissproducts.

The problem of the treatment of minerals containing metals associatedwith arsenic is the economical separation of the arsenic from the otheringredients without injurious results. Arsenical fumes are so difficultto condense on a large scale and so deleterious to the workmen andthesurrounding country that the presence of arsenic in many oresconstitutes a great practical drawback to their profitable utilization.

This invention has for its object a simple method of separating thearsenicv from the other ingredients by which practically the whole ofthe arsenic is obtained in a form very suitable for industrialutilization while on the other hand the residual substances are left ina good condition for further treatment. Few arsenical minerals aresufliciently free from gangue to admit of the profitable directapplication of the present process; and in order to obtain products of auniform character and specially suited to the operation of this -method,a preliminary smelting is desirable. The effect of this smelting will bethat the iron and other metals present are partly separated with thearsenic in the form of speiss. There are, however, instances in which anative mineral occurs which is a sufficiently pure arsenic to admit ofdirect treatment without any preliminary smelting.

The process according to the resent invention is conducted substantiay.as follows. The mineral or speiss is first ground to fine powder andthis should be sifted to eliminate any metallic particles or coarsefragments. The resulting Vmaterial in fine powder is then intimatelymixed with a sufficiency of soda ash or other suitable formLof sodiumcarbonate, in suchl proportions that a sli ht excess of alkali will bepresent after al owing for the combination with all the arsenic present.The mixture is then carefully roasted in a suitable calcining furnaceuntil the whole of the arsenic has become oxidized and has combined withthe alkali, forming anhydrous arseniate of soda, the iron and othermetals present formerly combined with the arsenic becoming oxidizedlikewise. The course of the operation in the calcining furnace may beexplained briefly in the following way: Assuming for instance that theore consists of diarsenid of iron FeAs this when heated will probablybecome reduced to-Fe As and arsenic will be liberated. Novolatilizationof the arsenic takes place at'any stage in the process, but the arsenicwill be oxidized in the presence of hot air, and by contact with thesoda it will form sodium arsenite (Na O) As O This ra idly takes .upmore oxygen and becomes so ium arseniate (Na O) As O The sodiumarseniate formed in the early stages of the process then reacts in allprobability with some of thereduced arsenid of iron'Fe As so as to formferrous arsenite (FeO) As O while the sodium arseniate in contactbecomes reduced to arseniate and is probably at once reoxidized by theair present. -The ferrous arsenite, the formatlon of which seemsprobable as an intermediate product, then absorbs oxygen giving Fe O andFe O while As O is formed; this latter is at once fixed by the soda and.further oxidized by at mospheric oxygen to give sodium arseniate, (Na O)As O which is the final product. It will be understood that this is onlythe robable course of the reaction and it w 1 be modified according tothe condition of affairs in the furnace, and according to the metalspresent. were cobalt and nickel, the resulting metallic oxids wouldrobably be the rotoxids, for the higher oxids of these meta s are notproduced in the roasting operation. In every case, however, the arsenicwill be converted ultimately into a soluble alkaline arseniate. Whenthis combination of the arsenic with the alkali has taken lace, theroasted product is leached and thoroughly washed with water, andractically the whole of the arsenic is disso ved out as arseniate ofsoda; The iron and other metals For instance if the metals left in theresidue are in the form of partially hydrated oxids. This condition isan ideal one for subsequent chemical solution.

The solution containing arseniate of soda may then be sim ly boiled insuitable iron or other pans until the evaporation has roceeded far enouh to give, on cooling a so. idified product. Pf desired of course theheating may be continued until a crude anhydrous product is obtained,and these products may be purified by recrystallization, or otherwise.

As an example of the process it may be mentioned that from an orecontaining about 40% of arsenic, an anhydrous arseniate of soda wasobtained, after the roasting and leaching, and this contained 44% ofarsenic acid, while the dried residual oxids retained only 2% ofarsenic. Theresults Willvary of course with the ore treated.

What I claim is:

1. Process for recovering arsenic from ores and speiss, consisting inmixing material containing alkaline carbonate with the materialcontaining the arsenic, roasting the mixture in the presence of. air,and dissolving out from the product the resulting salt consisting of thealkaline arseniate.

2. Process for recovering arsenic from ores and speiss, consisting inreducing the material containing the arsenic to the form of a powder,mixing material containing alkaline carbonate with the materialcontaining the arsenic, roastingthe mixture, and dissolving out from theproduct, the resulting salt containing the arsenic.

3. Process for recovering arsenic from ores and speiss, consisting inmixing material containing alkaline carbonate with the materialcontaining the arsenic in such quantity that there is, a slight excessof alkaline material beyond the quantity required to combine with allthe arsenic present, roasting the mixture, and dissolving out from theproduct the resulting salt containing the arsenic.

4. Process for recovering arsenic from ores and speiss, consisting inreducing the material containing the arsenic to the form of a powder,mixing material containing alkaline carbonate with the materialcontaining the arsenic in such quantity that there is a slight excess ofalkaline material beyond the quantity required to combine with all thearsenic present, roasting-the mixture, and dissolving out from theproduct the resulting salt containing the arsenic.

5. Process for recovering arsenic from ores and speiss, consisting inmixing material containing sodium carbonate with the material containingthe arsenic, roasting the mixture, and leaching the product whereby theresulting arseniate of soda is dissolved out.

6. Process for recovering arsenic from ores and speiss, consisting inmixing material containing sodium carbonate with the material containingthe arsenic, roasting the mixture whereby the arsenic is caused tocombine with the sodium as arseniate of soda while the metals present inthe original material are oxidized, leaching and then thoroughly washingthe product whereby the bulk of the arsenic is recovered and the residueis left with the metals in the form of partly hydrated oxids.

7. Process for recovering arsenic from ores and speiss, consisting inmixing material containing alkaline carbonate with the materialcontaining the arsenic, roasting the mixture, dissolving out from theproduct the resulting salt containing the arsenic, and recovering thearsenic from the solution thus obtained by evaporating it down andallowing the arseniate salt to solidify.

8. Process for recovering arsenic from ores and speiss, consisting inmixing material containing sodium carbonate with the material containingthe arsenic, roasting the mixture, dissolving out from the product theresulting arseniate of soda, and recovering the arsenic from thesolution thus obtained by evaporat ing it down and allowing the sodiumarseniate to solidify.

9. Process for recovering arsenic from ores and speiss, consisting inmixing ground soda ash with the material containing the arsenic,roasting the mixture, and leaching the product whereby the resultingarseniate of soda is dissolved out.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

T. BURNS MGGHIE.

Witnesses:

HUBERT A. GILL, A. E. ODELL.

